Many tremolo devices for electric guitars are known and available to those skilled in the guitar art. Though a useful and expressive tool for the electric guitarist, existing tremolo devices designed for use with electric guitars contain common faults that limit if not prevent their use with acoustic guitars.
One such fault is that the design of existing tremolo devices is such that the device alters the sound of an acoustic guitar in a manner considered undesirable to those skilled in the guitar art. As is well known, the sound produced by a standard acoustic guitar are significantly influenced by the manner in which the strings make contact with the fixed bridge of the guitar, as well as by the materials from which the fixed bridge is made. It is important that the bridge plate be formed of a porous, wooden material in order to produce the resonant characteristics considered acceptable for acoustic guitar tone.
Citing U.S. Pat. Nos. 2,741,146 to C. L. Fender, and 4,171,661 to Floyd Rose, as examples of prior art, it may be seen that customary construction of tremolo devices consists of a bridge plate of a metal material that differs greatly from the porous, wooden material necessary to produce acceptable acoustic guitar tone. Moreover, the soft nature of the porous wooden material needed to produce acceptable acoustic guitar tone from the guitar bridge is insufficiently strong to withstand the upwards of 400 pounds of stress exerted upon it by the combined tension of the strings and tremolo counterbalancing springs during the rocking motion of said bridge plate against fixed pivots necessary to accomplish the goal of raising and lowering the tension of the guitar strings to produce the desired tremolo effect.
It may also be observed in the sound-producing qualities of a standard fixed acoustic guitar bridge that one continuous string saddle of a width appropriate to span all strings on the guitar, made of bone, plastic or other material is friction-fit into a slot in the bridge plate so that the saddle contacts the bridge plate on all surfaces excepting the top surface. The strings, under tension, contact the top surface of the string saddle producing a downward force upon said string saddle, which in turn transfers the vibration of the strings into the bridge plate through all the points of contact that the string saddle makes with the bridge plate, creating acceptable acoustic guitar tone.
In the above cited patents, it will be noted that the customary practice for tremolo device design is to provide individual metal string saddles for each string on the guitar. The saddles are held against the top surface of the metal bridge plate in U.S. Pat. No. 2,741,146 by string tension and in U.S. Pat. No. 4,171,661 by a screw through each saddle. Neither of these customary methods are capable of transferring the vibration of the guitar string through the bridge plate in a manner consistent with the production of acceptable acoustic guitar tone.
Another fault of existing tremolo devices is that attachment of the device to the acoustic guitar places excessive stress on the top sound board of the acoustic guitar sound box. This in turn promotes the failure of the top board. It is customary for the top of the sound box of an acoustic guitar to be constructed from spruce or other similar soft wood in a thickness of no greater than 1/8 inch. When properly supported by suitable braces located on the underside of the top, spruce or other similar soft wood is able to withstand upwards of 200 lbs. of pull exerted by the strings at the site of a standard fixed bridge. It should be noted that the stress applied to the top by the tension of the strings is absorbed by the entire surface area where the standard fixed bridge and top join, thus spreading the stress over an area of sufficient size to withstand the tension without causing the top to fail.
The customary method for attaching a tremolo device to an electric guitar is by threading screws at least 1/2 inch in length into the top surface of a solid body guitar as anchors for the tremolo device base plate, as described in U.S. Pat. Nos. 2,741,146 and 4,171,661. The tremolo bridge is then pulled against the screws by the tension of the strings. The screws, which are perpendicular to the top of the guitar body, must absorb the full tension of the strings as well as remain upright against the rocking motion of the tremolo bridge when the device is in use. In a solid body guitar, there exists sufficient wood surrounding the screws to allow use and mounting of the tremolo device without damage to the body of the instrument.
Regarding an acoustic guitar, however, as will be clear to those skilled in the art, spruce (the type of material used for acoustic guitars), as referenced in Machinery's Handbook, 21st edition, under "Permissible Working Stresses for Structural Timbers (U.S. government tests)", has the ability to withstand compression of 250 p.s.i. perpendicular to the grain of the timber. And, in the thickness required for acoustic guitars, i.e., 1/8 inch or less, spruce, with this compression rating, is unable to support the screws necessary for mounting a tremolo device without severe damage to the top sound board of an acoustic guitar. Further, the spruce top, with a rating of 250 p.s.i. against compression perpendicular to the grain, and a thickness of 1/8 inch or less, cannot withstand the combined stress of 400 lbs. of tension placed against the mounting screws by the strings and tremolo counterbalancing springs. This would cause the mounting screws to move from the perpendicular position required for the tremolo device to operate properly.
Accordingly, the prior art devices are incapable of or at the very least impracticable for use with acoustic guitars.